Behaviour Of Cold-formed Steel Beams Research Articles

Numerical analysis of cold‐formed steel sigma-shaped beams in fire conditions

This paper presents the development of a finite element model for predicting the flexural behavior of cold-formed steel beams subjected to fire and with restrained thermal elongation (different grades of axial and rotational restraint). The numerical simulations were carried out with the finite element software Abaqus/CAE. The numerical model was compared with experimental results in order to validate it for further parametric studies. This paper provides details of the simulation methodology for achieving the numerical stability and faithful representation of detailed structural behavior. To verify the accuracy of the Abaqus model the numerical and experimental results were compared in terms of axial restraining forces, vertical mid-span deflections, critical temperatures and failure modes of the beams. The numerical results showed a good agreement with the experimental ones. However, the critical temperatures determined numerically were slightly lower than the numerical ones in the simply supported and axially restrained beams and the opposite in the axially and rotationally restrained beams, this for both sigma and 2-sigma section beams.

Experimental validation of the Direct Strength Method for shear spans with high aspect ratios

Shear behaviour of cold-formed steel beams with an aspect ratio (shear-span/web-depth) of 1.0 has been studied thoroughly, mainly using central point load tests. However, for beams with higher aspect ratios, the effect of bending causes a reduction of shear capacity and alters the failure modes. This paper introduces a new test setup, the dual actuator test rig, which is equipped with two actuators moving independently at customizable displacement rates to control and minimize applied bending moments in the shear spans of interest. Shear strength close to pure shear capacity can be therefore reached even at an aspect ratio of 2.0. Experimental series recently performed at the University of Sydney on channel section members using the new test configuration is presented. The experimental results together with other available experimental data are combined and used to validate and re-calibrate the Direct Strength Method design formulae incorporated in the AISI S100:2016 Specification and the AS/NZS 4600:2018 Standard.

Flexural behaviour of cold-formed steel beams filled with GGBS concrete and wrapped with GFRP

The popularity of the cold-formed sections has increased in recent years due to ease of fabrication and high strength-to-weight ratios. As the cold-formed hollow sections are normally thin, local buckling occurs before yielding of the sections, but it can be prevented by filling the sections with concrete. The load carrying capacity will be increased by wrapping the sections with glass fibre reinforced polymer (GFRP). This paper presents the flexural behaviour of cold-formed steel beams with and without concrete filling as well as with and without GFRP wrapping. Ten experiments were conducted and it is found that the load carrying capacity of concrete in-filled beams wrapped with GFRP performs better when compared to other cases. Numerical analysis carried out using ANSYS workbench 15.0 also proves that beams in-filled with concrete and wrapped with GFRP have better load carrying capacity.

Experimental study of shear strength of cold-formed channels with an aspect ratio of 2.0

Shear behaviour of cold-formed steel beams with an aspect ratio (shear span/web depth) of 1.0 has been studied thoroughly, mainly using central point load tests. However, for beams with longer aspect ratios, the effect of bending causes reduction of shear capacity and alters the failure modes. This paper summarises experiments recently performed at the University of Sydney on channel section members using a new test configuration to minimize bending moments. Shear strength close to pure shear capacity can be therefore reached even at an aspect ratio of 2.0. The test results were compared with the strength predictions using the current direct strength method (DSM) of design for shear specified in the North American specification for the design of cold-formed steel structural members, AISI S100:2016 and the Australian/New Zealand Standard for cold-formed steel structures, AS/NZS 4600:2018. A good agreement between the experimental results and the predicted values has confirmed the viability of the DSM design rules for structures with aspect ratios up to 2.0. Numerical models were developed to foresee potential issues prior to the experimental work, and were subsequently calibrated against the tests to produce reliable results.

Numerical simulation and experimental investigation on static behavior of cold formed steel beam with trapezoidally corrugated web by varying depth-thickness ratio

This paper presents a numerical simulation and experimental investigation on the static behavior of cold-formed steel beams with trapezoidally corrugated web has been carried out to find its structural performance of simply supported beam under pure bending. The steel beams with corrugated steel webs represent a new innovative which has emerged in the past decade for short- and medium-span beams. The thin corrugated web affords a significant weight reduction of these beams, compared with hot-rolled beams. In the initial solution, the flanges are made of flat plates, welded to the trapezoidal web sheet, requiring a specific welding technology. The connecting between flanges to the web can be done by means of intermittent welding. The paper summarizes the experimental and numerical investigations carried out at the Hindustan University and, at the end, presents the flexural behavior of cold-formed steel beams with trapezoidally corrugated web. To find the effect of web corrugation, 12 experiments were conducted on cold-formed steel beams. Beams having two different web depth-thickness (dw/tw) ratio 60 and 80 and with three types of web corrugation angles 0°, 30° and 45° were tested. Two beams were tested in each series. The static performance of the three different corrugation angles, including failure mode, load–deflection curves, strength capacity, load–strain curves, moment–curvature curves, flexural stiffness and ductility, are compared and discussed in detail based on the experimental results. Finally, numerical analysis using ANSYS Workbench results are analyzed and the experimental results were validated with the results obtained from the finite element analysis.

Flexural behaviour of axially and rotationally restrained cold-formed steel beams subjected to fire

This paper presents the results of a wide-ranging experimental research carried on the flexural behaviour of cold-formed steel beams subjected to fire. The main purpose of this work was to evaluate the influence of different cross-sections, especially of compound cold-formed steel sections, the axial restraint to the thermal elongation of the beam and the rotational stiffness of the beam supports. The results showed above all that the critical temperature of a cold-formed steel beam might be strongly affected by the stiffness of the surrounding structure depending on the relation between its stiffness and the stiffness of the beam.

Flexural behaviour of cold-formed steel beams in fire situation

Flexural behaviour of cold-formed steel beams in fire situation

Web crippling failure using quasi-static FE models

This paper presents an investigation on the use of quasi-static analyses with explicit integration to evaluate the web crippling behaviour of cold-formed steel beams. Web crippling failure occurs due to the application of transverse concentrated loads, which can be applied statically or dynamically. In the majority of the examples found in the literature, the web crippling phenomenon has been investigated by means of purely static shell finite element (SFE) models with implicit integration. In this work, the ABAQUS code was employed to implement SFE models aimed at replicating an experimental test and quasi-static analyses with an explicit integration scheme were adopted. First, a brief literature review on the topic of the numerical investigation of web crippling of cold-formed steel members is presented. Then, the paper addresses the characterisation of the quasi-static analysis concept with particular emphasis on the control of dynamic effects and the SFE model of a lipped channel beam under External Two Flange (ETF) loading is described. Several conventional parameters of standard SFE analysis, such as the SFE type, mesh selection, steel model, hardening effects due to cold-forming, residual stresses, initial imperfections and support conditions are explained, as well as additional specifications pertaining to the adoption of quasi-static analyses, such as the load rate, mass scaling, contact and friction, smoothed amplitude curves and inhibition of inertia (noise) effects. Finally, the results obtained are presented in the context of the ETF case, including load–displacement curves, curves of kinetic-to-internal energy ratio vs. displacement and beam deformed shapes (failure modes). It is concluded that explicit analysis leads to rigorous simulations of experimental test results, in terms of ultimate load, post-collapse load–deflection curve and failure mechanism. The failure mode obtained with the quasi-static analysis provides a better approximation of the one observed experimentally than its non-linear static analysis counterpart. Indeed, the failure mechanism emerges considerably more clearly when the quasi-static analysis is adopted.

Experimental and numerical analysis on the structural behaviour of cold-formed steel beams

A research study on the structural behaviour of cold formed steel beams with C-, I-, R- and 2R-shaped cross-sections at ambient temperature is presented, based on the results of a large programme of experimental tests and numerical simulations. Firstly, several four-point bending tests were carried out in order to assess mainly the failure loads and failure modes of the beams. Secondly, a suitable finite element model was developed to compare with the experimental results, and finally, a parametric study was undertaken in order to investigate the influence of the thickness, height and length of the beams on its structural behaviour.

Local and distortional buckling of cold-formed steel beams with both edge and intermediate stiffeners in their compression flanges

The true buckling behaviour of cold-formed steel beams with both edge and intermediate stiffeners in their compression flanges has been predicted with the aid of advanced numerical modelling. A series of nonlinear finite element analyses has been carried out to investigate the flexural behaviour of cold-formed Z sections with both edge and intermediate stiffeners in their flanges, when the failure is controlled by local and/or distortional buckling. The effect of the size and position of intermediate stiffeners as well as the effect of the edge stiffener/intermediate stiffener interaction on the buckling behaviour and ultimate strength of these sections has been studied. The knowledge gained from FE analyses was used to check the accuracy of the Eurocode design rules in predicting the ultimate strengths for these sections.

Local and distortional buckling of cold-formed steel beams with edge-stiffened flanges

The economic use of cold-formed steel members means that buckling and the possible loss of effectiveness it produces are important features of design. The prediction of the true buckling behaviour of cold-formed steel beams accounting for all governing features such as geometrical imperfections, material nonlinearity, postbuckling etc. has been possible with the development of advanced numerical modelling. The FE models developed in previous research have been used in this paper to investigate the effect of edge stiffeners (lips) and their interaction with compression flanges on the postbuckling of laterally restrained cold-formed Z-section beams. Depending on the lip size-to-flange width ratio and angle of inclination of the edge stiffener, the cross-sectional bending resistance varied and transitions between local, distortional and combined local/distortional buckling were observed. The suitability of the design treatments available in Eurocode 3 (EC3) for local and distortional buckling of cold-formed Z-section beams was assessed. Overall, the EC3 predictions for cross-sectional bending resistances were unconservative. Some shortcomings were identified and some suggestions for improvements were made. This included improvements in plate buckling factors for edge-stiffened compression flanges.

Global optimum design of cold-formed steel hat-shape beams

Using the computational neural network model developed recently by the authors, a comprehensive parametric study is performed for global optimization of cold-formed steel hat-shape beams based on the AISI Specifications. Design curves are presented for global optimum values of the thickness, the web-depth-to-thickness ratio, and the flange width-to-thickness ratio for unbraced beams having steel yield strengths of 250 and 345 N/mm 2. The computational neural network model guarantees a local optimum solution. The global optimum is found by an exhaustive search that is guided by a heuristic approach to reduce the search effort. An extensive parametric study yielded insights into the behavior of cold-formed steel beams that are then used as rules to reduce the search space and guide the exhaustive search. The procedure for finding the global optimum design of cold-formed steel beams is presented in a few recursive steps. The optimum design curves presented in this article can be of great value to structural design engineers.

Cold-formed steel webs with openings: Summary report

Based on a 3-year study that focused on the behavior of cold-formed steel beams with web openings, researchers at the University of Missouri Rolla have developed simple, easy, to apply design recommendations. The design recommendations address the limit states of web buckling resulting from bending, shear, web crippling, combined bending and shear, and combined bending and web crippling. The recommendations were developed based on the results of experimental and analytical studies of C-section beams. The C-sections, which are commonly used for wall studs and floor joists, are manufactured with web openings. Common web opening sizes are 38 × 102 mm and 19 × 51 mm. All web openings are located at mid-depth of the web and spaced 61 cm on center along the length of the C-section.

Analysis of thin-walled structures by finite strip and finite layer methods

The finite strip and finite layer methods are powerful tools for the analysis of thin-walled structures. In this paper, the finite strip method is applied to study the behavior of cold-formed steel beams including webs with longitudinal stiffeners. Comparisons are made with AISI specifications and published data. The finite layer method is used to investigate the buckling behavior of sandwich panels with thin facings and rigid foam cores. Effects of variable core stiffnesses (due to uneven curing, etc.) on the buckling strength are quantified and presented.

Cold-Formed Steel Members with Perforated Elements

In cold-formed steel structural members, holes are sometimes provided in webs, or flanges, or both of beams and columns for duct work, piping, ease of handling, and for other purposes. The presence of such holes may result in a reduction in strength of individual component elements or the overall strength of the member, or in both. At present, only a limited amount of design information is available for relatively heavy steel sections with perforated elements; however, no provisions are included in the American Iron and Steel Institute specification for the design of cold-formed steel members with perforated elements. The structural behavior of cold-formed steel beams and columns with a single circular or square hole in the web or flange has been studied in this preliminary investigation. Design formulas subject to a limited scope have been developed from this study for possible determination of effective design width and load-carrying capacities.